This invention relates in general to producing an image of a portion of a photographic image by using digital image processing.
For many decades, traditional commercial photofinishing systems have placed limits on the features offered to consumers to promote mass production. Among those features that are unavailable conventionally, zooming and cropping have been identified by both consumers and photofinishers as extremely useful additional features that could potentially improve the quality of the finished photographs and the subsequent picture sharing experiences. With the advent of, and rapid advances in digital imaging, many of the technical barriers that existed in traditional photography no longer stand insurmountable.
Hybrid and digital photography provide the ability to crop undesirable content from a picture, and magnify or zoom the desired content to fill the entire photographic print. In spite of the fact that some traditional cameras with zoom capability provide consumers greater control over composing the desired scene content, studies have found that photographers may still wish to perform a certain amount of cropping and zooming when viewing the finished photograph at a later time. Imprecise viewfinders of many point-and-shoot cameras, as well as simply second-guessing their initial compositions, are factors in the desirability of zoom and crop. In addition, it may be desirable to use some other regular border templates such as ovals, heart shapes, squares, etc. In another scenario, some people commonly referred to as xe2x80x9cscrapbookersxe2x80x9d tend to perform more aggressive crop in making a scrapbook, e.g., cutting along the boundary of objects.
There are significant differences in objectives and behaviors between these two types of cropping, namely album-making and scrapbook making, with the latter more difficult to understand and summarize. The invention described below performs automatic zooming and cropping for making photographic prints. One customer focus group study indicated that it would be beneficial to provide customers a double set of printsxe2x80x94one regular and one zoom. Moreover, it is preferred that the cropping and zooming be done automatically. Most customers do not want to think about how the zooming and cropping is being done as long as the content and quality (e.g., sharpness) of the cropped and zoomed pictures is acceptable.
There has been little research on automatic zoom and crop due to the apparent difficulty involved in performing such a task. None of the known conventional image manipulation software uses scene content in determining the automatic crop amount. For example, a program entitled xe2x80x9cXVxe2x80x9d, a freeware package developed by John Bradley at University of Pennsylvania, USA (Department of Computer and Information Science), provides an xe2x80x9cautocropxe2x80x9d function for manipulating images and operates in the following way:
the program examines a border line of an image, in all of the four directions, namely from the top, bottom, left and right sides;
the program checks the variation within the line. In grayscale images, a line has to be uniform to be cropped. In color images, both the spatial correlation and spectral correlation have to be low, except for a small percentage of pixels, for the line to be qualified for cropping. In other words, a line will not be cropped if it contains a significant amount of variation;
if a line along one dimension passes the criterion, the next line (row or column) inward is then examined; and
the final cropped image is determined when the above recursive process stops.
This program essentially tries to remove relatively homogeneous margins around the borders of an image. It does not examine the overall content of the image. In practice, the XV program is effective in cropping out the dark border generated due to imprecise alignment during the scanning process. However, disastrous results can often be produced due to the apparent lack of scene understanding. In some extreme cases, the entire image can be cropped.
Another conventional system, described by Bollman et al. in U.S. Pat. No. 5,978,519 provides a method for cropping images based upon the different intensity levels within the image. With this system, an image to be cropped is scaled down to a grid and divided into non-overlapping blocks. The mean and variance of intensity levels are calculated for each block. Based on the distribution of variances in the blocks, a threshold is selected for the variance. All blocks with a variance higher than the threshold variance are selected as regions of interest. The regions of interest are then cropped to a bounding rectangle. However, such a system is only effective when uncropped images contain regions where intensity levels are uniform and other regions where intensity levels vary considerably. The effectiveness of such a system is expected to be comparable to that of the XV program. The difference is that the XV program examines the image in a line by line fashion to identify uniform areas, while Bollman examines the image in a block by block fashion to identify uniform areas.
In summary, both techniques cannot deal with images with nonuniform background.
In addition, in the earlier invention disclosed in U.S. patent application Ser. No. 09/490,915, filed Jan. 25, 2000, the zoom factor needs to be specified by the user. There is, therefore, a need for automatically determining the zoom factor in order to automate the entire zoom and crop process.
Some optical printing systems have the capability of changing the optical magnification of the relay lens used in the photographic copying process. In U.S. Pat. No. 5,995,201, Sakaguchi describes a method of varying the effective magnification of prints made from film originals utilizing a fixed optical lens instead of zoom lens. In U.S. Pat. No. 5,872,619, Stephenson et al. describe a method of printing photographs from a processed photographic filmstrip having images of different widths measured longitudinally of the filmstrip and having heights measured transversely of the filmstrip. This method uses a photographic printer having a zoom lens and a printing mask to provide printed images having a selected print width and a selected print height. In U.S. Pat. No. 4,809,064, Amos et al. describe an apparatus for printing a selected region of a photographic negative onto a photosensitive paper to form an enlarged and cropped photographic print. This apparatus includes means for projecting the photographic negative onto first and second zoom lenses, each of the zoom lenses having an adjustable magnification. In U.S. Pat. No. 5,872,643, Maeda et al. describe a film reproducing apparatus that can effectively perform zoom and crop. This apparatus includes an image pick-up device which picks up a film frame image recorded on a film to generate image data, an information reader which reads information about photographing conditions of the film frame image, and a reproducing area designator which designates a reproducing area of the film frame image. However, the reproducing area of the film frame image is determined based on pre-recorded information about the position of the main object, as indicated by which zone of the photograph the automatic focusing (AF) operation in the camera was on-part of the recorded information about photographing conditions. In all the above-mentioned optical printing systems, the position of the photographic film sample and magnification factor of the relay lens are pre-selected.
According to the present invention, there is provided a solution to the problems of the prior art. It is an object of the present invention to provide a method for producing a portion of a photographic image by identifying the main subject of the photographic image.
According to a feature of the present invention, there is provided a method of producing an image of at least a portion of a digital image, comprising the steps of:
a) providing a digital image having pixels;
b) computing a belief map of the digital image, by using the pixels of the digital image to determine a series of features, and using such features to assign the probability of the location of a main subject of the digital image in the belief map;
c) determining a crop window having a shape and a zoom factor, the shape and zoom factor determining a size of the crop window; and
d) cropping the digital image to include a portion of the image of high subject content in response to the belief map and the crop window.
One advantage of the invention lies in the ability to automatically crop and zoom photographic images based upon the scene contents. The digital image processing steps employed by the present invention includes a step of identifying the main subject within the digital image. The present invention uses the identified main subject of the digital image to automatically zoom and crop the image. Therefore, the present invention produces high-quality zoomed or cropped images automatically, regardless whether the background is uniform or not.